July, 2014 Volume 24, Number 5

In This IssueWeed of the Month: Toothed Spurge (Euphorbia dentata) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Plant Diagnostic Clinic Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Weather Data for the Week Ending July 28 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

&Integrated PestCrop Management

Figure 1. Toothed spurge is one species that has been found with increasing frequency in Missouri soybean fields in recent years.

Continued on page 2 u

Weed of the Month: Toothed Spurge (Euphorbia dentata)by Kevin Bradley

Toothed spurge, Euphorbia dentata, is a summer annual that is native to the eastern United States and Mexico . The plant is also referred to as wild poinsettia but this common name is more properly suited to a close relative of toothed spurge, Euphorbia heterophylla . Wild poinsettia (Euphorbia heterophylla) is a very common weed throughout much of Central America and now also occurs in the southern U .S . from Florida to California, but I have not personally encountered it in Missouri yet . Toothed spurge is one weed that I have seen more of over the past several years in Missouri cropping systems . I would not consider it a common weed yet by any means, but one that has increased in prevalence over the past several seasons,

July, 2014 2 Volume 24, Number 5

Weed of the Month: Toothed Spurge (Euphorbia dentata)by Kevin Bradley

especially in Missouri soybean fields . Toothed spurge can also be found in pastures, along roadsides, and in other non-crop areas .

Toothed spurge can reach up to 2 feet in height and has stems that are light green to reddish green with short hairs . The leaves can be either opposite or alternately arranged along the stem and are from ¾ to 3 inches in length and up to 1 inch in width . The leaves are elliptic to ovate in outline with toothed margins . Leaves occur sparsely along the lower stems but are bunched or whorled near the upper portions of the plants . The upper leaf surfaces are dark green and without hairs, while the lower leaf surfaces are light to medium green and can have short hairs along the veins . The leaves and stems emit a white milky sap when broken . This milky latex sap is poisonous and can produce blisters and dermatitis in humans, cattle, and horses, and can also cause blindness if it comes in direct contact with the eye . The stems terminate in a flat-topped cluster of flowers . Each cluster consists of a mixture of flowers and immature fruits . The flowers are without petals or sepals and are yellow, pink, or white . Toothed spurge typically blooms in mid-summer and the blooming period lasts for about 1 month . After blooming, the flowers are replaced with 3-lobed nodding fruits . The fruits can become light red to purple with maturity . Each fruit contains 3 seeds that are oval in shape and dark brown to black in color . The roots consist of a taproot with a fibrous root system .

Toothed spurge is tolerant to normal use rates of glyphosate, which is more than likely the reason why we have seen more of it in Missouri cropping systems in recent years . The appearance of toothed spurge is an example of a weed shift, which is what occurs when producers rely predominantly on one herbicide or one weed management system to meet all their weed control needs . After continuous application of the same herbicide, in this case glyphosate for post-emergence weed control, species that are naturally tolerant of that herbicide are most likely to appear in that cropping system and become more prevalent . Also, toothed spurge does not typically emerge until later in the season, and in this way “escapes” the residual effects of many pre-emergence residual herbicide treatments .

Unfortunately, there is little information available on the control of toothed spurge in corn and soybeans . What little information I have found indicates that in corn, atrazine and isoxaflutole (Balance Pro, Balance Flexx) provide good pre-emergence control, while dicamba (Banvel, Clarity, Status, Distinct, etc .), glufosinate (Liberty), and a tank-mix of bromoxynil (Buctril) plus atrazine can provide good post-emergence control . In soybean, flumioxazin products (Valor, Fierce, Envive, etc .) have good pre-emergence activity, while lactofen (Cobra, Phoenix) and a tank-mix of imazethapyr (Pursuit) plus bentazon (Basagran) have been shown to provide good post-emergence control . Liberty in Liberty Link soybean is also an option . In both corn and soybean, a single post-emergence application of glyphosate will likely only provide about 50 to 60% control of toothed spurge . Although it is unlikely that complete control will ever be achieved with glyphosate, control can be increased to approximately 70 or 80% with two applications of glyphosate, but toothed spurge seed production will almost certainly still occur .

Figure 2. Toothed spurge has leaves that are elliptic to ovate in outline and exude a milky sap when broken.

Figure 3. A young toothed spurge plant.

July, 2014 3 Volume 24, Number 5

The Plant Diagnostic Clinic has been re-opened for 2 months now . It has been a whirlwind of activity and a lot of learning on my part . I am grateful for all the assistance I’ve received from specialists in the Division of Plant Sciences and University of Missouri Extension . This write up highlights fruit, vegetable, ornamental and turf samples submitted . Two graphs are included to show the activity in the Plant Diagnostic Clinic thus far (Figure 1 and Figure 2) .

Fruits and VegetablesThere have been several issues diagnosed on fruit

samples . Winter injury was reported in both blackberry and blueberry . There has been some chemical injury reported on blueberry, blackberry, apple, pear and cherry due to drift from neighboring fields, accidental sprays from the grower or misapplication of fertilizer causing a phytotoxicity . Reporting on diseases, this spring has been a big fire blight year across the state of Missouri . The spring weather was perfect for this . Walking around the MU-Columbia campus there isn’t a Bradford pear tree that isn’t affected . For fruit-producing and ornamental trees, affected by fire blight, pruning is recommended . The MU-Extension publication, G6020, on fire blight is useful to learn about the disease and recommendations (http://extension .missouri .edu/p/g6020) .

Other disease issues include:

Crop Disease / Pest / IssueBlueberry Alternaria leaf spot

Phomopsis twig blight

Pear Cedar-hawthorne rustFire bligh

Strawberry Rhizoctonia crown rotGray moldCalcium deficiency

Watermelon Bacterial fruit blotchGummy stem blight

Blackberry Nutrient deficiency

Apple Fire blight

A handful of vegetable samples have been submitted, mostly tomatoes . Many of these have had chemical injury . Chemical injury has also been diagnosed on spaghetti squash and potato . The most common injuries are due to a growth regulator herbicide . In some cases the grower used an herbicide between rows or in close proximity . However,

in most of the cases the grower is positive they have not made an herbicide application . During the investigation, the source of damage is commonly the compost or manure used in the soil . Many growers don’t think about the potential of herbicide carryover in manure or compost (straw, grass clippings or even wood chips) .

There is an article from a MU extension specialist (http://extension .missouri .edu/nwregion/hort/current/herbicide .shtml) and an article from North Carolina State University (http://www .ces .ncsu .edu/fletcher/programs/ncorganic/special-pubs/herbicide_carryover .pdf) that covers this topic .

Diseases and issues diagnosed are listed below:Crop Disease / Pest / Issue

Garlic Bacterial soft rot

Tomato Bacterial canker, Bacterial stem rot, Undetermined virus, Gray mold, Pythium root rot, White mold, Southern blight, Frost injury, Physiological leaf roll, Juglone toxicity

OrnamentalsA number of cases of winter injury on ornamentals was diagnosed this spring. Many woody orna-mentals were already stressed going into winter from the 2013 drought. A reminder that when the weather is hot and dry, supplemental watering to woody ornamentals is recommended. The common story with the evergreens is, they stayed green all winter long and when temperatures warmed up dieback was noticed. Green tissues turned brown practically overnight, or so it seems. The reason is that evergreens do not go into complete dormancy during the winter. During warm, sunny days the plants are still biologically active, reduced but still transpiring and using water. If the plants don’t have enough water stored in their roots or if the ground is frozen making water unavailable, they become stressed. Since biological activity is re-duced the plants will retain their green color. How-ever, once the weather warms up and the plants go back to their full photosynthetic potential the dead parts are quickly abscised (cut off from receiving any water or nutrients), leaving branches, leaves or needles yellow and unaesthetically pleasing.

Plant Diagnostic Clinic Updateby Patricia Wallace

July, 2014 4 Volume 24, Number 5

The dead branches should be pruned as they can attract bark beetles or other insects. Plant species diagnosed with winter / cold injury include arbor-vitae, blue atlas cedar, pines (white pine the most prevalent), rhododendron and a tulip tree. There has also been a number of chemical injuries, which include drift from neighboring agronomic fields or misapplications by the homeowner or landscaping company.

Plant diseases and pests diagnosed include:Ornamental Disease / Pest / Issue

Boxwood Boxwood mites

Cypress tree Pestalotia canker

Geranium Gary mold, Bacterial blight, Nutrient deficiency

Maple Bacterial blight

River birch Anthracnose

Weeping willow Black cancer

TurfgrassTurfgrass samples have been submitted from golf courses, parks, schools and lawns. The majority of these samples have come from golf putting greens, due to their need for intensive and aggressive man-agement practices. Submitted plant species includ-ed creeping bentgrass, fescue, Kentucky bluegrass, and Zoysia grass.

The diseases and issues are listed below:Type of turfgrass Disease / Pest / Issue

Bentgrass Pink snow moldYellow patchAnthracnosePythium root rotBlue green algaeNematodes

Fescue Aphids, Sand abrasion

Kentucky bluegrass Septoria leaf spotPythium root rot

Zoysia Large patch

Figure 1: Services requested at the PDC.

Figure 2: Types of plants submitted to the clinic for disease identification.

Plant Diagnostic Clinic Updateby Patricia Wallace

July, 2014 5 Volume 24, Number 5

Weather Data for the Weekly Period July 22 - July 28, 2014

Station County

Weekly Temperature (oF)Monthly

Precipitation (in.)Growing

Degree Days‡

Avg.Max.

Avg.Min.

ExtremeHigh

ExtremeLow Mean

Departurefrom longterm avg.

May1-28

Departurefrom longterm avg.

Accumulated Since Apr 1

Departurefrom longterm avg.

Corning Atchison 89 67 99 58 78 +1 2.86 -1.92 2137 +189

St. Joseph Buchanan 86 68 94 60 77 0 4.54 +0.35 2006 +71

Brunswick Carroll 86 66 93 57 77 +1 2.91 -0.95 2142 +168

Albany Gentry 86 65 93 58 76 -1 3.50 -1.07 1950 +51

Auxvasse Audrain 86 63 94 55 75 -2 1.81 -1.79 2010 +9

Vandalia Audrain 84 62 91 56 73 -4 3.56 -0.47 1964 +19

Columbia-Bradford Research and Extension Center

Boone 86 64 93 58 75 -3 1.60 -2.01 1998 -54

Columbia-Capen Park Boone 90 63 97 57 76 -2 1.87 -2.22 2024 -97

Columbia-Jefferson Farm and Gardens

Boone 87 65 93 60 76 -2 1.86 -1.75 2052 -4

Columbia-Sanborn Field Boone 88 67 95 61 77 -1 1.75 -2.00 2178 +53

Columbia-South Farms Boone 86 65 93 59 76 -2 1.88 -1.79 2029 -24

Williamsburg Callaway 87 62 94 54 75 -2 1.64 -2.13 2021 +74

Novelty Knox 82 62 91 56 72 -4 2.01 -1.85 1853 -69

Linneus Linn 85 65 93 59 75 -1 2.01 -2.41 1921 +32

Monroe City Monroe 83 62 92 55 73 -4 3.48 -0.12 1944 -26

Versailles Morgan 90 66 95 58 78 0 1.32 -2.42 2156 +52

Green Ridge Pettis 87 66 93 58 77 0 1.81 -2.00 2043 +23

Lamar Barton 91 68 99 61 79 0 1.05 -3.24 2175 -6

Cook Station Crawford 90 62 100 54 77 -1 1.01 -2.16 2065 -43

Round Spring Shannon 90 61 97 54 75 -2 1.89 -1.52 1987 -34

Mountain Grove Wright 87 64 94 60 75 -2 2.68 -0.90 1934 -37

Delta Cape Girardeau 85 62 93 56 74 -5 2.86 +0.13 2155 -218

Cardwell Dunklin 87 66 92 60 76 -4 3.49 +0.50 2407 -184

Clarkton Dunklin 87 65 93 59 76 -4 2.30 -0.86 2341 -208

Glennonville Dunklin * * * * * * * * * *

Charleston Mississippi 86 65 93 58 76 -3 1.94 -1.25 2375 -12

Portageville-Delta Center Pemiscot 87 67 93 62 77 -3 4.39 +1.54 2465 -108

Portageville-Lee Farm Pemiscot 87 67 93 61 77 -3 3.22 +0.12 2482 -74

Steele Pemiscot 88 66 94 61 77 -3 3.47 +0.55 2404 -182

‡Growing degree days are calculated by subtracting a 50 degree (Fahrenheit) base temperature from the average daily temperature. Thus, if the average temperature for the day is 75 degrees, then 25 growing degree days will have been accumulated.

Weather Data provided by Pat GuinanGuinanP@missouri.edu

(573) 882-5908

Insect Pest & Crop Management newsletter is published by the MU IPM Program of the Division of Plant Sciences Extension . Current and back issues are available on the Web at http://ipm.missouri.edu/ipcm/ . Mention of any trademark, proprietary product or vendor is not intended as an endorsement by University of Missouri Extension; other products or vendors may also be suitable .

Editor: Amy Hess (hessa@missouri .edu)